1. Field of the Invention
The present invention relates to an ion plating device and an ion plating method.
2. Description of the Related Art
Film formation by Ion plating is performed by supplying a constant voltage to the inside of a vacuum chamber to generate a discharge plasma from a material of a film and by applying the plasma to a substrate placed in the vacuum chamber to deposit the film on the substrate.
Such film formation by ion plating is employed in film formation on various types of substrates, such as coating of a reflection film on a mirror. FIG. 4 is a schematic view showing a structure of an example of a device for forming a film by the ion plating.
Referring to FIG. 4, an ion plating device 60 comprises a vacuum chamber 61, a substrate holder 62 placed in the vacuum chamber 61 for holding the substrate 65, a vaporizing source 63 for holding a material of a film and vaporizing the material in the vacuum chamber 61, a radio frequency (RF) power supply 66 for supplying predetermined power to the inside of the vacuum chamber 61 via the substrate holder 62, and a direct current (DC) power supply 67 for supplying a constant negative bias voltage to the inside of the vacuum chamber 61 via the substrate holder 62.
The material vaporized by the vaporizing source 63 is changed into a plasma 68 by power supplied by the RF power supply 66 and the DC power supply 67 and an ionized material contained in the plasma 68 is deposited on the substrate 65 as the film, thus forming the film on the substrate 65.
By application of the bias voltage by the DC power supply 67, the ions tends to acceleratively migrate toward the substrate 65 and the film can be made dense. Also, by application of the bias voltage, a film strongly adhered to the substrate 65 can be formed. Particularly when the voltage output from the DC power supply 67 is higher, it is possible to make the film denser and more strongly adhered to the substrate 65.
However, it is proved that arcing is likely to occur in the vacuum chamber 61 when the bias voltage is applied as described above. In addition, it is proved that the arcing is more likely to occur especially when the bias voltage is higher. It is considered that the arcing occurs as follows.
When the bias voltage is applied, the ions in the plasma 68 tend to be drawn toward the substrate holder 62 and be spatially biased. When the substrate 65 situated between the vaporizing source 63 and the substrate holder 62 or the film formed on the substrate 65 is made of an insulating material, or the material of the film is the insulating material, the ions are captured by the insulating material, and its vicinity is not electrically neutralized, causing a large electric field to be locally formed. For this reason, breakdown of the insulating material occurs, causing arcing.
Particularly when the substrate 65 or the film on the substrate 65 is made of the insulating material, the ions tend to be captured in the vicinity of the substrate 65 or on the film, which causes the arcing to occur in the vicinity of the substrate 65 or on the film. When the arcing occurs, impurities tends to be mixed into the film in formation of the film on the substrate 65, causing uniformity or density of the film to be reduced. When a path of the arcing penetrates through the film formed on the substrate 65, the film is damaged.